Acoustic signal-based positioning systems may be used with mobile devices such as smartphones, tablets, and laptops. Moreover, acoustic signal-based positioning systems may be used with basically any computing device that has a screen. One example of an acoustic signal-based positioning system is a digital pen having an acoustic signal transmitter that is in communication with a receiver that is a computing device, wherein the digital pen is used to interact with the computing device. A conventional acoustic signal-based positioning system includes a transmitter that emits acoustic signals and a receiver which receives the emitted signals. The receiver measures the propagation time delay, referred to as Time of Arrival (“TOA”), of the received acoustic signal, and may multiply the TOA by the speed of sound, to determine a position of the transmitter. Using multiple receivers may allow triangulation and/or another form of multilateration, and provide for the determination of a position in two or even three dimensions.
Acoustic positioning systems that determine a position based on a time delay may also be synchronized or non-synchronized. Synchronized systems may use a synchronization signal that has a speed that is faster than the speed of sound and is transmitted to the receiver for synchronizing the clocks of the transmitter and receiver. Non-synchronized systems may use multiple receivers for receiving the emitted acoustical signal and calculating a Differential Time of Arrival (“DTOA”) that is a time delay measured between the multiple receivers. Generally, synchronized systems may be less susceptible to errors and less affected by temperature, calibration errors, and/or time delay errors.
Accordingly, there is a need for an improved synchronization system for acoustic signal-based positioning systems that have low power requirements, do not require dedicated synchronization hardware and are easy to implement in a variety of electronic devices.